The subject invention is directed toward the art of pipe joints and couplings and, more particularly, to an improved tube coupling. The coupling of the invention is particularly suited for use in ultra-high vacuum applications and will be described with reference thereto; however, it should be appreciated that the invention is capable of broader application and could be used in different fluid systems under operating under a variety of conditions.
In U.S. Pat. No. 3,521,910 to Callahan, et al. there is disclosed a tube coupling which has achieved commercial success and is widely used in both pressure and vacuum operations. It does, however, find widespread acceptance for use in ultra-high vacuum applications.
The coupling of the noted patent generally comprises first and second annular coupling components having axial through passages and end faces which extend perpendicular to the axis of the passages. The end faces provide sealing surfaces for the coupling end and typically include an annular rib, or bead-like protuberance generally of hemispherical cross-section, which extends outwardly from each end face about the through passage. Typically, a smooth, flat annular meral sealing gasket is trapped between the opposed end faces. A threaded coupling nut or nuts act to drive the coupling components toward one another to produce sealing engagement of the annular ribs with opposite side faces of the annular sealing gasket. During make-up of the coupling, it is highly preferable that relative rotation between the coupling components and the sealing washer be minimized. That is, it is desirable to suppress or eliminate any such relative motion which could produce undesirable scoring or gauling of the sealing washer and/or the sealing end faces. Such scoring or galling can drastically reduce the effectiveness of the joint. In fact, under certain circumstances, leaks can develop and the ability to remake the joint after disassembly can be lost.
In an effort to prevent the relative rotation and reduce torques transmission from the coupling nut to one or the other of the coupling components, it has been proposed to install anti-friction thrust bearings between the coupling nut and the associated coupling component. The driving forces from the coupling nut to the coupling components are thus directed through the thrust bearings. Hopefully, the bearings transmit the forces without the transmission of torque to the coupling components. Both standard and special ball and needle type thrust bearing assemblies have been used for this purpose.
Although the thrust bearing approach has been somewhat satisfactory, it is generally undesirable in that it significantly increases the cost and complexity of the coupling assemblies. Moreover, the addition of the anti-friction thrust bearings can significantly increase the overall length of the coupling assemblies. Accordingly, there has existed an ongoing need for a design to prevent relative rotary movement between the sealing faces of the coupling components and/or between the coupling components and the seal ring.